Pneumatic press

ABSTRACT

A pneumatic punch press having a frame including a bed adapted to support one press tool and a ram adapted to carry another press tool and supported on the frame for vertical reciprocable movement relative to the bed. The ram is biased away from the bed by a pair of parallel springs and is moved in the direction thereof by a pair of parallel fluid actuators connected between the frame and the ram. -each actuator has a hollow, flexible, thin-walled shell defining a pneumatic fluid chamber of variable volume. A pneumatic control circuit provides fluid connection between each of the chambers and a source of pneumatic fluid pressure whereby pressure in each chamber may be varied to expand each shell in one direction and contract it in another direction to effect movement of the ram toward the bed. In accordance with another embodiment of the invention, a plurality of fluid actuators connected in series and end-to-end relation effect movement of a ram.

United States Patent Yarlott et al. Nov. 28, 1972 PNEUMATIC PRESS 72 Inventors: John M. Yarlott, West Bare Hill [57] ABSTRACT Rd.; John C. Gray, Bolton Road, both of Harvard, Mass. 01451 Filed: Oct. 7, 1970 Appl. No.: 78,683

References Cited UNITED STATES PATENTS l/1966 Pucci et al. ..83/639 X 11/1944 Duffy etal ..lOO/269 A 4/1968 De Beckett et al. 100/269 A Primary ExaminerAndrew R. Juhasz Assistant Examiner-Leon Gilden Attorney-McCormick, Paulding and Huber A pneumatic punch press having a frame including a bed adapted to support one press tool and a ram adapted to carry another press tool and supported on the frame for vertical reciprocable movement relative to the bed. The ram is biased away from the bed by a pair of parallel springs and is moved in the direction thereof by a pair of parallel fluid actuators connected between the frame and the ram. Oeach actuator has a hollow, flexible, thin-walled shell defining a pneumatic fluid chamber of variable volume. A pneumatic control circuit provides fluid connection between each of the chambers and a source of pneumatic fluid pressure whereby pressure in each chamber may be varied to expand each shell in one direction and contract it in another direction to effect movement of the ram toward the bed. In accordance with another embodiment of the invention, a plurality of fluid actuators connected in series and end-to-end relation effect movement of a ram.

PATENTEDHHYZB 912 4 3. 703. 84 2 89 so We 1 INVENTORS r JOHN M. YARLOTT 7 7e 72 74 JOHN c. GRAY M ATTORNEYS PNEUMATIC PRESS BACKGROUND OF THE INVENTION This invention relates in general to pneumatic machines and deals more particularly with an improved pneumatic press or the like driven by a flexible, pressure responsive pneumatic actuator.

The general aim of the present invention is to provide an improved press or like machine which is durable, reliable, safe to operate and which may be manufactured at relatively low cost. A further aim of the invention is to provide a pneumatic drive conversion unit adapted to replace the existing drive unit on a press or like machine to increase efficiency and safety of the machine by eliminating various vulnerable parts thereof such as conventional clutches and brakes.

SUMMARY OF THE INVENTION In accordance with the present invention, an improved pneumatic press or like machine is provided which includes a frame supporting a movable part or ram for reciprocating movement relative thereto and at least one actuator having a hollow, flexible, thin-walled shell defining a pneumatic fluid chamber of variable volume having opposing end portions adapted for movement toward and away from each other between retracted and extended positions in response to variation of pneumatic fluid pressure in the chamber. Movement of the actuator is controlled by a pneumatic circuit communicating with the chamber and with a pneumatic fluid pressure source. Means are provided for connecting the actuator between the frame and the ram to effect movement of the ram in response to variation of the pressure in said chamber. Apparatus made in accordance with the present invention is also provided to replace the existing drive unit on a press or like machine having a frame and a reciprocating part or ram.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front elevational view of a press embodying the present invention.

FIG. 2 is a side elevational view of the press of FIG. 1.

FIG. 3 is a schematic view of the press of FIG. 1.

FIG. 4 is a schematic view of another apparatus embodying the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to the drawing and referring particularly to FIGS. 1-3, a punch press embodying the present invention and indicated generally at comprises a frame 12 supporting a vertically reciprocably movable part or ram 14 which is driven in one direction by a pair of pressure responsive pneumatic fluid actuators indicated generally at 16, 16. The actuators are connected between the frame and the ram and are activated by a pneumatic control circuit indicated generally at 17 and connected to a pneumatic fluid pressure source 18.

The illustrated press 10 exemplifies a conventional press which has been converted for pneumatic operation in accordance with the present invention. Consequently, the frame 12 and the ram 14 comprise parts of a punch press of a type which ordinarily includes a conventional drive mechanism having a crank shaft, connecting rod and flywheel. However, in the illustrated case, the conventional drive mechanism has been removed from the press and a pneumatic drive unit embodying the present invention has been substituted therefor. The frame may take various forms, but, as shown, it comprises a metal casting which includes a base or bed 19 and a pair of side members 20, 20 which project upwardly from the bed. A cross brace 22 connects the upper ends of the side members to impart rigidity to the frame structure. The ram 14 is disposed between and supported by the side members 20, 20 for vertically sliding movement relative to the bed 19 by guideways or slides 24, 24, respectively defined by the side members 20, 20. The ram is adapted to carry a tool or punch 26 which is movable therewith into and out of operative relation with another tool or die 28 mounted on the bed 19. When the ram 14 is in its first position, as it appears in full lines in FIGS. 1 and 2, the punch 26 is out of operative relation with the die 28. Operation of the control circuit 17 causes the ram to move from its first position to a second position, indicated by broken lines, to move the punch into operative relation with the die.

Connection between the ram 14 and the actuators 16, 16 is provided by a connecting member indicated generally at 30. The connecting member includes a generally rectangular link 32 which surrounds the cross brace 22. The link has upper and lower portions thereof respectively indicated at 33 and 34 and disposed above and below the cross brace 22. Connection between the upper end of the ram 14 and the link lower portion 34 is provided by a threaded connecting rod 35 which facilitates vertical adjustment of the ram relative to the connecting member 30 whereby the operative position of the punch 26 may be adjusted relative to the die 28. The connecting member 30 also includes a cross member 36 connected to the link portion 33 by an upright member 38. The free end portions of the cross member 36 extend transversely outwardly in opposite directions beyond the link 32. A pair of guide rods 40, 40 fastened to the frame 12 extend upwardly therefrom at opposite sides of the link 32 and pass through the cross member 36. Each guide rod 40 has a nut 42 secured to the upper end thereof to limit upward travel of the connecting member 30. Each guide rod 40 also has an axially elongated coil spring 44 coaxially received thereon. The springs 44, 44 act between the frame 12 and the connecting member 30 to bias the ram 14 upwardly toward its first position. The maximum cross-sectional dimension of each guide rod 40 is approximately equal to the inside diameter of the coil spring 44 received thereon. Thus, in the event of spring breakage, an associated guide rod will cooperate with a broken spring to prevent total collapse of the spring, thereby limiting the drop or fall of the ram. This arrangmment safe guards the operator in the event that spring breakage should occur as the operator is manually feeding a work piece into or removing a work piece from the press.

The pressure responsive actuators 16, 16 convert pneumatic fluid energy input to mechanical output and may take various forms. A typical actuator 16, illustrated in FIG. 2, comprises an axially elongated flexible, thin-walled shell 46 which defines a pressure chamber 48 of variable volume. The shell has coaxially aligned coupling members 50 and 52 secured to opposite end portions thereof. The coupling member 50 is attached to an associated free end portion of the cross member 36. The coupling member 52 is secured in a fixed position by a bracket 54 fastened to the frame. An inlet passageway 56 in the coupling member 52 opens through the wall of the shell 46 and communicates with the chamber 48 and provides fluid connection between the chamber and the control circuit 17, as best shown in FlG. 3. The shell 46 is adapted for radial expansion and axial contraction in response to changes in pressure in the chamber 48. Axially extended and retracted positions of the shell 46 respectively indicated by full and broken lines in FIG. 1, respectively correspond to the first and second positions of the ram 14. The shell 46 is preferably formed from an elastomeric material suitably reinforced so that the surface area thereof remains substantially constant both in its axially extended and retracted positions. Thus, substantially all fluid energy input is consumed in moving the coupling member 50 toward the coupling member 52 and little or no energy is expended in stretching the shell material. In its axially retracted or inflated condition, the actuator 16 is characterized by a generally prolate spheroidal configuration. When the actuator 16 is in its axially retracted position, the shell 46 has a generally convoluted cross-sectional configuration characterized by a plurality of circumaxially spaced ridges and valleys. The shell 46 is biased to its axially extended position and movable to its retracted position in response to a predetermined pressure pulse received in the chamber 48 from the pneumatic circuit 17. In the illustrated case, biasing force for retaining the actuators l6, 16in axially extended position is provided by the springs 44, 44. Each actuator 16 is preferably adapted to operate in response to an applied pressure of fifteen pounds per square inch. A more complete disclosure of the presently preferred actuator is found in US. Pat. No. 3,645,173, issued to John M. Yarlott, Ser. No. 867,463, filed Oct. 20, 1969, and entitled Fluid Actuator. Fluid actuators made in accordance with the latter U.S. patent are manufactured and marketed by Trish Energetics, lnc., Harvard, Massachusetts.

The control circuit includes at least one pneumatic fluid pressure accumulator for containing a charge of pneumatic fluid or pressurized air and at least one pilot valve for releasing the charge from the accumulator to the actuators. In the illustrated case, the control circuit 17 includes a pair of pressure accumulators 58, 58 and a pair of pilot valves 60, 60. Each pilot valve 60 has an inlet port 62, an outlet port 64 and an exhaust port 66 and is connected between one of the accumulators 58, 58 and an associated actuator 16. The valves 60, 60 are arranged to operate simultaneously, or at least substantially simultaneously, to release a pressure pulse from each accumulator 58 to its associated actuator 16 to effect operation thereof. Preferably, and as shown, simultaneous operation of the pilot valves 60, 60 is efiected by operation of an associated auxiliary control circuit indicated generally at 68 and which may, for example, include a pair of manually operable control buttons 70, 70 or the like which must be simultaneously operated to effect operation of the pilot valves.

Considering the control circuit 17 in further detail, the accumulators 58, 58 are connected to the source 18 by a supply air line 72 and branch lines 74, 74. A pneumatic pressure regulator 76 in the line 72 is provided to maintain a constant air supply pressure for the control circuit 17. An air filter 78 positioned in the supply line 72 downstream of the regulator 76 assures a supply of clean air to the circuit 17. Metering orifices 80, 80 positioned in the branch lines 74, 74 regulate air flow from the source 18 to the accumulators 58, 58. Each accumulator 58 is connected to the inlet port 62 of an associated pilot valve 60. Each outlet port 64 is connected to an associated inlet passageway 56 and communicates with an associated chamber 48. A bleed port 82 is provided in the circuit between each valve and its associated actuator 16. Each bleed port 82 has an associated metering orifice 84 therein for regulating flow of bleed or exhaust air therefrom.

At the start of each operating cycle, each pilot valve 60 is positioned with its outlet port 64 in communication with its exhaust port 66 and its inlet port 62 in a closed position. Accordingly, the air pressure within each chamber 46 is substantially equal to atmospheric pressure and the actuators 16, 16 are biased to their axially extended positions by the springs 44, 44. At the start of each operating cycle, each accumulator 58 contains a charge of air under pressure sufficient to effect operation of an associated actuator 16. Operation of the auxiliary control circuit 68 by manually operating the control buttons 70, causes the valves 60,60 to simultaneously shift positions so-that the inlet port 62 of each valve is connected to the outlet port 64 thereof and the exhaust port 66 of each valve is in a closed position. The charges of pressure fluid contained in the accumulators 58, 58 are simultaneously released therefrom and flow into and through thepilot valves 60, 60 and into the chambers thereby inflating the actuators. I

The sudden pressure pulses released by the two pressure accumulators cause the two actuators to rapidly expand thereby accelerating the ram 14 in a downwardly direction and bringing the punch 26 into operative relation with the die 28. The inertia of the ram, of course, contributes energy at the end of the down stroke. If the control circuit is arrangedso that the ram remains in its second position while the control buttons 70, 70 remain depressed, air under pressure will, of course, flow from the source 18 to the accumulators 58, 58 and to and through the pilot valves 60, 60 to the actuators 16, 16. However, the relationship between the orifices or restrictions 80, and 84, 84 are such that air will be bled or exhausted from the control circuit 17 through the bleed ports 84, 84 at substantially the same rate at which the air enters the accumulators 58, 58 through the orifices 80, 80. Thus, the orifices 80, 80 cooperate with the orifices 84, 84 to 4 prevent excessive pressure buildup within the cham- 80, 80 also function to retard actuator recovery time by delaying pressure build-up therein. Thus, upon completion of one cycle the press cannot repeat or immediately recycle. This arrangement provides an added degree of security for the press operator. In the event of actuator leakage or rupture, the springs 44, 44 immediately return the ram 14 to its first position so that the press will fail safe.

The operational characteristics of the press will be determined by such variables as the mass of the ram, its stroke and the operational characteristics of the actuator or actuators which drive it.

Another machine embodying the present invention is illustrated somewhat schematically in FIG. 4 and indicated generally by the reference numeral 10a. The machine 10a is similar in some respects to the machine previously described and parts of the machine 10a which correspond to parts of the machine 10 bear the same reference numerals and a suffix letter a and will not be hereinafter further described.

The machine 10a has a frame 12a and a reciprocably movable ram 14a adapted to be driven by at least one fluid actuator. However, in the illustrated case, a group of series connected actuators, which includes three fluid actuators 16a, 16a drives the ram 14a. A lever 88 pivotally connected to the frame 12a and to the ram 14a provides means for connecting the actuators 16a, 16a between the frame and the ram. The free end portion of the lever 88 carries a counterweight 90 which provides means for biasing the ram 14a to a first position indicated by full lines. The ram is moved to its second or broken line position by operation of the actuators 16a, 16a which are connected in axial alignment and in end-to-end relation. Each actuator 16a has a fluid pressure chamber 48a of variable volume and is movable between axially extended and retracted positions, as previously discussed. The actuators are connected together so that the chambers thereof are in communication with each other, substantially as shown. Fluid pressure is supplied to the actuators 16a, 160 by a fluid control circuit 17a which includes a fluid pressure accumulator 58a having sufficient volume to contain a charge for inflating all of the actuators in the group. The charge is received from a source 19a and is released by a pilot valve 60a associated with the circuit 17a in the manner substantially aforedescribed. Each actuator acts through a relatively limited distance in moving from its axially extended position to its axially retracted position. Thus, when a machine is powered by a single actuator, the effective stroke of its moving part is somewhat limited. However, it will be evident that the stroke of a machine embodying the present invention may be substantially increased by arranging the actuators thereof in connected series relation as illustrated in FIG. 4. When a group of actuators are so arranged, the effective working distance of the group will be equal to the sum of the working distance of each of the actuators in the group.

The present invention has been described with reference to a punch press and another machine of like kind. However, it will be evident that the machine drive structure herein disclosed and claimed may be advantageously applied to machines for performing other operations, as for example, crimping, riveting, fastening and stitching, and such modified machine forms are contemplated within the scope of the invention.

We claim:

1. A pneumatic press comprising a frame including a bed for supporting one tool, a ram adapted to carry another tool and supported on said frame for movement generally toward and away from said bed between a first position wherein the other tool is spaced from the one tool and a second position wherein the other tool is in operative relation with the one tool, means for biasing said ram toward said first position, at least one fluid actuator having an axially elongated hollow flexible thin-walled shell defining a pneumatic fluid chamber of variable volume and including generally axially opposed end portions, said end portions being movable between axially extended and axially retracted positions in response to variation of pneumatic fluid pressure in said chamber, said shell having a surface of substantially constant area in all of said positions, said surface in said axially extended position having a fluted configuration characterized by a circumaxially spaced series of axially extended ridges and valleys, said shell in said axially retracted position having a generally prolate spheroidal configuration, means for securing one of said end portions in fixed position relative to said frame, means connecting the other of said end portions to said ram for moving said ram from said first to said second position in response to movement of said end portions to said axially contracted position, and means providing a circuit adapted for connection to a pneumatic fluid pressure source for controlling flow of pneumatic pressure fluid received from the source into and from said chamber to vary the volume of said chamber and effect movement .of said end portions between said axially retracted and extended positions, respectively.

2. A pneumatic power conversion unit for a press having a frame including a bed for supporting one tool, means associated with said frame and defining a guideway having one end thereof generally aligned with said bed, and a ram adapted to carry another tool and supported by said guideway for movement between a first position wherein the other tool is spaced from the one tool and a second position wherein the other tool is in operative relation with the one tool, said conversion unit comprising means for biasing said ram toward said first position, at least one fluid actuator having an axially elongated hollow flexible thin-walled shell defining a pneumatic fluid chamber of variable volume and including generally axially opposed end portions, said end portions being movable between axially extended and axially retracted positions in response to variation of pneumatic fluid pressure in said chamber, said shell having a surface of substantially constant area in all of said positions, said surface in said axially extended position having a fluted configuration characterized by a circumaxially spaced series of axially extended ridges and valleys, said shell in said axially retracted position having a generally prolate spheroidal configuration, means for securing one of said end portions in fixed position relative to said frame, means connecting the other of said end portions to said ram for moving said ram from said first to said second position in response to movement of said end portions to said axially contracted position, and means providing a circuit adapted for connection to a pneumatic fluid pressure source for controlling flow of pneumatic pressure fluid received from the source into and from said chamber to vary the volume of said chamber and effect movement of said end portions between said axially retracted and extended positions, respectively.

3. A pneumatic press as set forth in claim 1 wherein said means for biasing said ram comprises a spring acting between said frame and said connecting means.

4. A pneumatic press as set forth in claim 3 wherein said spring is further characterized as an axially elongated coil spring and including a guide rod having one end portion thereof secured in fixed relation to said frame and extending coaxially through said spring and through said connecting means.

5. A pneumatic press as set forth in claim 4 wherein said guide rod has a major cross-sectional dimension approximately equal to the internal diameter of said coil spring.

6. A pneumatic press as set forth in claim 1 wherein said frame includes a pair of transversely spaced side members projecting upwardly from said bed and a transversely extending cross brace providing connection between the upper ends of said side members, said ram is disposed between said side members and supported for general vertical movement between said first and second positions and said connecting means includes a link having portions thereof disposed above and below said cross brace.

7. A pneumatic press as set forth in claim 6 including a pair of fluid actuators, said connecting means including a transversely extending connecting member attached to the upper end of said link and projecting transversely outwardly in opposite directions therefrom and wherein each of said actuators is disposed at an opposite side of said link, said one end portion of each of said actuators being connected to said connecting member.

8. A pneumatic actuator as set forth in claim 7 wherein said fluid actuators are arranged in axially parallel relation to each other.

9. A pneumatic press as set forth in claim 18 wherein said one actuator has a fluid passageway therethrough communicating with said chamber and said circuit includes a pneumatic fluid pressure accumulator for receiving and containing a charge of pressure fluid sufficient to effect a single expansion of said chamber to move said end portions from said axially extended .to said axially retracted position, said accumulator being connected to said passageway to supply pressure fluid to said chamber and being adapted for connection to the pressure source to receive pressure fluid therefrom, and a pilot valve for controlling pressure fluid flow from said accumulator to said chamber and for; exhausting pressure fluid from said chamber.

10. A pneumatic press as set forth in claim 9 wherein said circuit includes metering means positioned between said accumulator and the pressure source for metering the flow of pressure fluid from the source to said accumulator.

11. A pneumatic press as set forth in claim 10 wherein said circuit includes a bleed port between said pilot valve and said actuator for bleeding pressure fluid from said circuit and said actuator to the atmosphere.

12. A pneumatic press as set forth in claim 1 1 wherein said bleed port is adapted to exhaust pressure fluid to the atmosphere and from said accumulator and said circuit at substantially the same rate at which ressure fluid flows through said metering means an into said accumulator.

13. A pneumatic press as set forth in claim 1 including a plurality of actuators connected in series and in end-to-end relation, said pressure chamber defined by each of said actuators communicating with said pressure chamber defined by the other of said actuators.

14. A pneumatic press as set forth in claim 1 wherein said connecting means comprises a linkage pivotally connected to said frame and pivotally connected to said ram.

15. A pneumatic press as set forth in claim 14 wherein said other end portion is connected to said linkage intermediate the pivotal connections between said frame and said ram.

16. A pneumatic press as set forth in claim 1 wherein said shell is made from elastomeric material reinforced to prevent change in the surface area thereof. 

1. A pneumatic press comprising a frame including a bed for supporting one tool, a ram adapted to carry another tool and supported on said frame for movement generally toward and away from said bed between a first position wherein the other tool is spaced from the one tool and a second position wherein the other tool is in operative relation with the one tool, means for biasing said ram toward said first position, at least one fluid actuator having an axially elongated hollow flexible thin-walled shell defining a pneumatic fluid chamber of variable volume and including generally axially opposed end portions, said end portions being movable between axially extended and axially retracted positions in response to variation of pneumatic fluid pressure in said chamber, said shell having a surface of substantially constant area in all of said positions, said surface in said axially extended position having a fluted configuration characterized by a circumaxially spaced series of axially extended ridges and valleys, said shell in said axially retracted position having a generally prolate spheroidal configuration, means for securing one of said end portions in fixed position relative to said frame, means connecting the other of said end portions to said ram for moving said ram from said first to said second position in response to movement of said end portions to said axially contracted position, and means providing a circuit adapted for connection to a pneumatic fluid pressure source for controlling flow of pneumatic prEssure fluid received from the source into and from said chamber to vary the volume of said chamber and effect movement of said end portions between said axially retracted and extended positions, respectively.
 2. A pneumatic power conversion unit for a press having a frame including a bed for supporting one tool, means associated with said frame and defining a guideway having one end thereof generally aligned with said bed, and a ram adapted to carry another tool and supported by said guideway for movement between a first position wherein the other tool is spaced from the one tool and a second position wherein the other tool is in operative relation with the one tool, said conversion unit comprising means for biasing said ram toward said first position, at least one fluid actuator having an axially elongated hollow flexible thin-walled shell defining a pneumatic fluid chamber of variable volume and including generally axially opposed end portions, said end portions being movable between axially extended and axially retracted positions in response to variation of pneumatic fluid pressure in said chamber, said shell having a surface of substantially constant area in all of said positions, said surface in said axially extended position having a fluted configuration characterized by a circumaxially spaced series of axially extended ridges and valleys, said shell in said axially retracted position having a generally prolate spheroidal configuration, means for securing one of said end portions in fixed position relative to said frame, means connecting the other of said end portions to said ram for moving said ram from said first to said second position in response to movement of said end portions to said axially contracted position, and means providing a circuit adapted for connection to a pneumatic fluid pressure source for controlling flow of pneumatic pressure fluid received from the source into and from said chamber to vary the volume of said chamber and effect movement of said end portions between said axially retracted and extended positions, respectively.
 3. A pneumatic press as set forth in claim 1 wherein said means for biasing said ram comprises a spring acting between said frame and said connecting means.
 4. A pneumatic press as set forth in claim 3 wherein said spring is further characterized as an axially elongated coil spring and including a guide rod having one end portion thereof secured in fixed relation to said frame and extending coaxially through said spring and through said connecting means.
 5. A pneumatic press as set forth in claim 4 wherein said guide rod has a major cross-sectional dimension approximately equal to the internal diameter of said coil spring.
 6. A pneumatic press as set forth in claim 1 wherein said frame includes a pair of transversely spaced side members projecting upwardly from said bed and a transversely extending cross brace providing connection between the upper ends of said side members, said ram is disposed between said side members and supported for general vertical movement between said first and second positions and said connecting means includes a link having portions thereof disposed above and below said cross brace.
 7. A pneumatic press as set forth in claim 6 including a pair of fluid actuators, said connecting means including a transversely extending connecting member attached to the upper end of said link and projecting transversely outwardly in opposite directions therefrom and wherein each of said actuators is disposed at an opposite side of said link, said one end portion of each of said actuators being connected to said connecting member.
 8. A pneumatic actuator as set forth in claim 7 wherein said fluid actuators are arranged in axially parallel relation to each other.
 9. A pneumatic press as set forth in claim 18 wherein said one actuator has a fluid passageway therethrough communicating with said chamber and said circuit includes a pneumatic fluid pressure accumulator for receiving and containing a chaRge of pressure fluid sufficient to effect a single expansion of said chamber to move said end portions from said axially extended to said axially retracted position, said accumulator being connected to said passageway to supply pressure fluid to said chamber and being adapted for connection to the pressure source to receive pressure fluid therefrom, and a pilot valve for controlling pressure fluid flow from said accumulator to said chamber and for exhausting pressure fluid from said chamber.
 10. A pneumatic press as set forth in claim 9 wherein said circuit includes metering means positioned between said accumulator and the pressure source for metering the flow of pressure fluid from the source to said accumulator.
 11. A pneumatic press as set forth in claim 10 wherein said circuit includes a bleed port between said pilot valve and said actuator for bleeding pressure fluid from said circuit and said actuator to the atmosphere.
 12. A pneumatic press as set forth in claim 11 wherein said bleed port is adapted to exhaust pressure fluid to the atmosphere and from said accumulator and said circuit at substantially the same rate at which pressure fluid flows through said metering means and into said accumulator.
 13. A pneumatic press as set forth in claim 1 including a plurality of actuators connected in series and in end-to-end relation, said pressure chamber defined by each of said actuators communicating with said pressure chamber defined by the other of said actuators.
 14. A pneumatic press as set forth in claim 1 wherein said connecting means comprises a linkage pivotally connected to said frame and pivotally connected to said ram.
 15. A pneumatic press as set forth in claim 14 wherein said other end portion is connected to said linkage intermediate the pivotal connections between said frame and said ram.
 16. A pneumatic press as set forth in claim 1 wherein said shell is made from elastomeric material reinforced to prevent change in the surface area thereof. 